Until the present invention, leads to be brazed onto braze pads of leadless IC packages have been positioned by means of a leadframe, from which the leads project inwardly in the plane of the frame, over the braze pads for brazing thereto. With this cantilever arrangement of leads, a positioning tolerance of +/-0.005 inches at the ends of the leads to be attached to the braze pads is difficult to improve upon. With fine pitch lead connections on ceramic packages, a positioning tolerance at the connection is desirably +/-0.002 inches. One proposal to achieve this positioning tolerance is to use a removable plastic support. However, such a method is relatively expensive, not totally effective and rather complex to achieve in view of the braze pad spacing on such fine lead pitch packages of only 0.025 inches center to center. In another prior art proposal, a snap-off tie bar which ties all of the leads together at their very tip is proposed. At the braze pads, the tie bar extends up off the ceramic package so that it may be snapped off after brazing. Each lead is necked down at its connection with the tie bar to allow the tie bar to be easily snapped off. A disadvantage of this arrangement is that the tie bar leaves only two sides of the lead exposed for brazing onto the braze pad with the end of the lead being prevented from forming part of the brazed joint because of its connection with the tie bar. In addition this arrangement leaves "pigtails" of metal after tie bar removal leading to handling and space utilization problems. Further, the tie bar concept requires special handling for removal of the tie bar and an additional step in the production of the leadframe because of the requirement that the tie bar be shaped to extend off of the ceramic package to facilitate its removal. The special handling for removal of the tie bar also involves additional steps.
It is known in the production of plastic IC packages, in which a leadframe is used to connect leads, which extend through the molded plastic package to the chip housed therein, to use a dam bar interconnecting the leads in the plane of the leadframe to act as a dam to limit the flow of plastic during injection molding of the package. This is necessary as the two mold halves are clamped together with the leads projecting through an opening between them thereby leaving gaps between the leads and the mold halves through which the plastic can extrude during molding. The dam bar prevents any significant flow of plastic resulting from this. The dam bar is then removed by punching operation and the small amount of extruded plastic projecting from the package is also removed.
It is an object of the present invention to provide enhanced lead alignment capable of providing the desired positioning tolerance between the ends of leads while they are brazed to braze pads of fine pitch ceramic IC packages and of improving dissipation of heat generated by this brazing.